1. Field of the Invention
The present invention relates to a photoelectric conversion element formed using a semiconductor and a semiconductor device including the photoelectric conversion element.
2. Description of the Related Art
As one mode of a photoelectric conversion element, a photoelectric conversion element having sensitivity to light with a wavelength of 400 to 700 nm in the visible light region is referred to as a light sensor or a visible light sensor. A known application of a light sensor or a visible light sensor is to detect a light signal and read information and to detect brightness of the ambient environment and control operation of electronic appliances or the like.
For example, a light sensor is used in a cellular phone or a television device so that brightness of a display screen is adjusted according to brightness of the ambient environment where the cellular phone or the television device is placed (see Patent Document 1: Japanese Published Patent Application No. 2002-62856).
FIG. 2A shows a structure of a light sensor disclosed in Patent Document 1. A photoelectric conversion layer 1603 is provided over a substrate 1601 so as to be interposed between a light-reflective electrode 1604b and a light-transmitting electrode 1602 provided with openings 1605 and 1606. The photoelectric conversion layer 1603 has a PIN junction and forms a diode in combination with the light-transmitting electrode 1602 and the light-reflective electrode 1604b. That is, the light sensor has a mode as a two-terminal element. One of external connection terminals is formed of a light-reflective electrode 1604a which is connected to the light-transmitting electrode 1602 through an opening 1607 provided in the photoelectric conversion layer 1603. The other is formed of the light-reflective electrode 1604b. A light-receiving surface is the light-transmitting substrate 1601 side, and light transmitted through the substrate 1601 is incident on the photoelectric conversion layer 1603.
FIG. 2B shows a light sensor in which a light-reflective electrode 1611, a photoelectric conversion layer 1612, and a light-transmitting electrode 1613 are provided in this order over a substrate 1610. This light sensor has a structure in which light is incident on the photoelectric conversion layer 1612 from the light-transmitting electrode 1613 side. Through holes are formed in the light-reflective electrode 1611 and the photoelectric conversion layer 1612, and insulating layers 1614 and 1615 are provided in the through holes. The insulating layers 1614 and 1615 prevents the short-circuit between the light-reflective electrode 1620 and the photoelectric conversion layer 1621, which are located in the neighborhood of an edge of the substrate 1610, and the light-reflective electrode 1611 and the photoelectric conversion layer 1612. The light-transmitting electrode 1613 and the light-transmitting electrode 1619 are electrically insulated from each other by an insulating layer 1616 provided over the photoelectric conversion layer 1612. An external connection terminal 1617 is provided so as to be in contact with the light-transmitting electrode 1619 and is electrically connected to the photoelectric conversion layer 1612 and the light-reflective electrode 1611. The other external connection terminal 1618 is provided so as to be in contact with the light-transmitting electrode 1613.
FIG. 2C shows a mode in which the light sensor shown in FIG. 2A is mounted on a wiring board 1800. The wiring board 1800 and the light sensor are fixed to each other by a photo-curing resin or thermosetting resin 1852 so that the light-reflective electrodes 1604a and 1604b face wirings 1850. The light-reflective electrodes 1604a and 1604b are electrically connected to the wirings 1850 by conductive particles 1851. In addition, FIG. 2D shows a mode in which the light sensor shown in FIG. 2B is mounted on the wiring board 1800. The wiring board 1800 and the light sensor are bonded to each other by a conductive material 1853 such as cream solder or silver paste so that the external connection terminals 1617 and 1618 face the wirings 1850.